In the related art, an image forming apparatus including a fixing device has been known which is configured to convey a recording sheet to the fixing device when the fixing device is at an appropriate temperature and to change supply timing of the recording sheet in accordance with the temperature of the fixing device so as to shorten time up to start of image formation.
For example, there is known an image forming apparatus having a control device configured to determine supply timing of the recording sheet. The control device is configured to set supply timing of a first recording sheet to a first timing on condition that a temperature gradient of the fixing device during predetermined time after a printing command is received is greater than a threshold value, and to set the supply timing of the first recording sheet to a second timing later than the first timing on condition that the temperature gradient is equal to or less than the threshold value. Also, the control device changes the threshold value to a smaller value when the temperature of the fixing device at the time of receiving the printing command is higher.
In the meantime, the time that is to be consumed until the fixing device at a cold state is heated to a fixable state changes depending on an output of a heater configured to heat the fixing device. For example, when a control of increasing the output of the heater is carried out at a state where the fixing device is cold, the heat is more likely to be transferred to the entire fixing device as compared to when a control of decreasing the output of the heater is carried out. As a result, the time that is to be consumed after the fixing device is heated until the fixing device becomes at a fixable state is shortened. For this reason, even when the temperature gradient of the fixing device during a predetermined time after the printing command is received is less than the threshold value, there are cases when the first recording sheet can be supplied at the first timing if the output of the heater is high.